This invention generally relates to humidity controllers and more particularly to a humidity controller for controlling, i.e., humidifying or dehumidifying, the interior of a chamber in which a magnetic disk or the like is housed.
Design of hard magnetic disk apparatuses in which the extent to which the magnetic head is floated above the surface of a magnetic disk is minimized, e.g., set to a value of 0.2 .mu.m or less, is now being studied. In such a magnetic disk apparatus designed for high-density recording, when the humidity inside the apparatus is higher than a certain level, there is a possibility of occurrence of local dew condensation which may cause the magnetic head and the magnetic disk to adhere to each other, thereby preventing the apparatus from operating. To cope with this problem, an improved humidity controller which is designed to electro-chemically decompose moisture inside the apparatus and to maintain a highly dehumidified state has been proposed.
FIG. 1 schematically shows in section an example of this type of conventional humidity controller disclosed in Japanese Patent Laid-Open No 62-277126. A chamber 1 in which a magnetic disk and a magnetic head (not shown) and other components are housed has an opening la. A humidity controlling element 2 is disposed in the opening 1a with an insulating member 3 interposed between the humidity controlling element 2 and the edge of the opening 1a. The insulating member 3 is formed by injection molding on the edge of the humidity controlling element 2. A dc power source 4 is connected to the humidity controlling element 2 to supply the same with a dc current. FIGS. 2(a) and (b) show details of the humidity controlling element 2 in plan and in section, respectively. The humidity controlling element 2 has a hydrogen ion conductor membrane 7, e.g., an ion exchange membrane made of a fluorine resin or, more specifically, Nafion (commercial name of a product of Dupont. Porous electrodes 8a and 8b which are porous platinum films are respectively formed by plating on the obverse and reverse surfaces of the hydrogen ion conductor membrane 7. Collecting electrodes 9a and 9b each in the form of a mesh are connected to surfaces of the porous electrodes 8a and 8b. Each of the collecting electrodes 9a and 9b is formed by partially cutting a titanium lamella alternately and finely and thereafter expanding the same to obtain an expanded metal. An anode terminal 10a and cathode terminal 10b are connected to peripheral portions of the collecting electrodes 9a and 9b.
The principle of dehumidification of the interior of the chamber will be schematically described below. After the power source 4 has been turned on, a dc current introduced through the anode terminal 10a spreads over the collecting electrode 9a having a high conductivity, then passes the porous electrode 8a, the hydrogen ion conductor membrane 7 and the porous electrode 8b, and reaches the other collecting electrode 9b. The current converges at this electrode, then flows out through the cathode terminal 10b and returns to the power source 4. The following decomposition reaction of water H.sub.2 O existing in the interior space of the chamber 5 first takes place at the interface between the porous electrode 8a and the hydrogen ion conductor membrane film 7: EQU H.sub.2 O.fwdarw.2H.sup.+ +1/2O.sub.2 +2e.sup.-
O.sub.2 caused by this decomposition stays in the interior of the chamber 5, and hydrogen ions H.sup.+ proceed to the porous electrode 8b through the hydrogen ion conductor membrane 7. Electrons e.sup.- are supplied from the collecting electrode 9a to the porous electrode 8a via the anode terminal 10a, the power source 4 and the collecting electrode 9b.
At the interface between the hydrogen ion conductor membrane 7 and the porous electrode 8b facing the outside 6, one or both of the following reactions take place between H+ ions moved through the hydrogen ion conductor membrane 7, electrons e.sup.- supplied through the collecting electrode 9b and O.sub.2 supplied from the outside 6 of the chamber: EQU 2H.sup.+ +1/2O.sub.2 +2e.sup.- .fwdarw.H.sub.2 O EQU 2H.sup.+ +2e.sup.- .fwdarw.H.sub.2
Water (H.sub.2 O) or H.sub.2 thereby generated is diffused on the outside 6 of the chamber. Thus, water is successively removed from the interior of the chamber.
In the above-described type of conventional humidity controller, the collecting electrodes 9a and 9b are respectively connected to the porous electrodes 8a and 8b by being disposed over the whole surfaces thereof. This is because, if the porous electrodes 8a and 8b having a comparatively large resistance are used alone, spreading and conversion of the current between the terminals 10a and 10b are not effected adequately, and the reaction is not effected uniformly over the hydrogen conductor membrane 7, resulting in difficulty in achieving the desired dehumidifying performance. The collecting electrodes 9a and 9b having a high conductivity are connected to the surfaces of the porous electrodes 8a and 8b in order to make the current flow uniform and stable.
Thus, the desired performance can be realized if the humidity controller is used at a certain temperature. However, the temperature inside the chamber 1 changes immediately after the magnetic disk apparatus has started or stopped operating. Since the linear expansion coefficient of the porous electrodes 8a and 8b (made of platinum) formed by plating on the hydrogen ion conductor membrane 7 differs from that of the collecting electrodes 9a and 9b (made of titanium), the collecting electrodes 9a and 9b, which have been in a normal state as shown in FIG. 3(a), are deformed and bent as the temperature is repeatedly changed. The connection between the collecting electrodes 9a and 9b and the porous electrodes 8a and 8b is broken over a large area, as shown in FIG. 3(b), if the change in temperature becomes about tens of degrees per hour. FIG. 4 shows the relationship between the maximum value of this bending for certain materials used as the collecting electrodes. The extent of bending varies depending upon the material, but, regardless of the material, disconnection causes a considerable reduction in the dehumidifying performance.